From: Michael Ellerman <mpe@ellerman.id.au> To: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>, Kees Cook <keescook@chromium.org> Cc: linux-kselftest@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>, Shuah Khan <shuah@kernel.org>, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] selftests/seccomp: fix ptrace tests on powerpc Date: Sun, 13 Sep 2020 22:34:23 +1000 [thread overview] Message-ID: <875z8hrh2o.fsf@mpe.ellerman.id.au> (raw) In-Reply-To: <20200911180637.GI4002@mussarela> Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: > On Tue, Sep 08, 2020 at 04:18:17PM -0700, Kees Cook wrote: >> On Tue, Jun 30, 2020 at 01:47:39PM -0300, Thadeu Lima de Souza Cascardo wrote: ... >> > @@ -1809,10 +1818,15 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee, >> > EXPECT_EQ(entry ? PTRACE_EVENTMSG_SYSCALL_ENTRY >> > : PTRACE_EVENTMSG_SYSCALL_EXIT, msg); >> > >> > - if (!entry) >> > + if (!entry && !syscall_nr) >> > return; >> > >> > - nr = get_syscall(_metadata, tracee); >> > + if (entry) >> > + nr = get_syscall(_metadata, tracee); >> > + else >> > + nr = *syscall_nr; >> >> This is weird? Shouldn't get_syscall() be modified to do the right thing >> here instead of depending on the extra arg? >> > > R0 might be clobered. Same documentation mentions it as volatile. So, during > syscall exit, we can't tell for sure that R0 will have the original syscall > number. So, we need to grab it during syscall enter, save it somewhere and > reuse it. I used the test context/args for that. The user r0 (in regs->gpr[0]) shouldn't be clobbered. But it is modified if the tracer skips the syscall, by setting the syscall number to -1. Or if the tracer changes the syscall number. So if you need the original syscall number in the exit path then I think you do need to save it at entry. cheers
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From: Michael Ellerman <mpe@ellerman.id.au> To: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>, Kees Cook <keescook@chromium.org> Cc: linuxppc-dev@lists.ozlabs.org, Shuah Khan <shuah@kernel.org>, Oleg Nesterov <oleg@redhat.com>, linux-kselftest@vger.kernel.org Subject: Re: [PATCH] selftests/seccomp: fix ptrace tests on powerpc Date: Sun, 13 Sep 2020 22:34:23 +1000 [thread overview] Message-ID: <875z8hrh2o.fsf@mpe.ellerman.id.au> (raw) In-Reply-To: <20200911180637.GI4002@mussarela> Thadeu Lima de Souza Cascardo <cascardo@canonical.com> writes: > On Tue, Sep 08, 2020 at 04:18:17PM -0700, Kees Cook wrote: >> On Tue, Jun 30, 2020 at 01:47:39PM -0300, Thadeu Lima de Souza Cascardo wrote: ... >> > @@ -1809,10 +1818,15 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee, >> > EXPECT_EQ(entry ? PTRACE_EVENTMSG_SYSCALL_ENTRY >> > : PTRACE_EVENTMSG_SYSCALL_EXIT, msg); >> > >> > - if (!entry) >> > + if (!entry && !syscall_nr) >> > return; >> > >> > - nr = get_syscall(_metadata, tracee); >> > + if (entry) >> > + nr = get_syscall(_metadata, tracee); >> > + else >> > + nr = *syscall_nr; >> >> This is weird? Shouldn't get_syscall() be modified to do the right thing >> here instead of depending on the extra arg? >> > > R0 might be clobered. Same documentation mentions it as volatile. So, during > syscall exit, we can't tell for sure that R0 will have the original syscall > number. So, we need to grab it during syscall enter, save it somewhere and > reuse it. I used the test context/args for that. The user r0 (in regs->gpr[0]) shouldn't be clobbered. But it is modified if the tracer skips the syscall, by setting the syscall number to -1. Or if the tracer changes the syscall number. So if you need the original syscall number in the exit path then I think you do need to save it at entry. cheers
next prev parent reply other threads:[~2020-09-13 12:34 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-30 16:47 [PATCH] selftests/seccomp: fix ptrace tests on powerpc Thadeu Lima de Souza Cascardo 2020-06-30 16:47 ` Thadeu Lima de Souza Cascardo 2020-09-08 23:18 ` Kees Cook 2020-09-08 23:18 ` Kees Cook 2020-09-11 18:06 ` Thadeu Lima de Souza Cascardo 2020-09-11 18:06 ` Thadeu Lima de Souza Cascardo 2020-09-13 12:34 ` Michael Ellerman [this message] 2020-09-13 12:34 ` Michael Ellerman 2020-09-17 22:37 ` Kees Cook 2020-09-17 22:37 ` Kees Cook 2020-09-17 22:51 ` Thadeu Lima de Souza Cascardo 2020-09-17 22:51 ` Thadeu Lima de Souza Cascardo 2020-09-18 6:22 ` Michael Ellerman 2020-09-18 6:22 ` Michael Ellerman
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